What/how does compression ratio affect an engine?

On Tue, 11 Dec 2007 01:55:38 +0000, Scott
wrote:

FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
LOT more than unleaded auto! Therefore, the 100 octane valves should be
supper lubricated! But, in fact, the 80 octane valve tend to stick if
much 100LL is run through them...

So, somebody answer my question...what is special about 100 octane
valves? The ones I put in my A-65 were Stellite. What does Stellite
do? What about sodium filled valves? What's their claim to fame??

Scott


Matt Whiting wrote:
Scott wrote:

Like I said, MIGHT OK, if there is no difference in heat, what are
the 100 octane valves in my A-65 for? Or more generally, why do they
sell 100 octane valves for A-65s and C-85s, etc. that were certified
on 80 octane??? Like I said, I use them, I don't wrench on 'em


Because valves that were designed to be lubricated by the lead in leaded
fuel may not last long when using fuel with no or less lead.

Matt


Scott

High octane fuel burns slower in low compression engines. This lets
the flame front go out the exhaust valves and burn them if you run a
lot of hours.

We ran into this in the 'old' days when the fighters used 115-145
octane fuel. If we used that fuel in our cars we had to mix some oil
with it to prevent the burnt valves.Occasionally someone would burn a
tank full to clean their engine out (burn carbon off cylinders and
valves, etc)

This is probably the reason they put 100 octane valves in your low
compression engine so you could use 100 octane and not destroy the
valves?

Big John

I understand your comment about the lack of lubrication from auto fuel,
but I was talking about 100LL...I never mentioned auto fuel in any of my
posts. I'm looking for an answer to why it was suggested that I put 100
octane valves in my A-65 if I was going to burn 100LL (I could have
replaced my valves with the standard 80 octane valves and continued to
burn auto fuel with Marvel Mystery oil mixed in for valve lubrication).

Scott


Matt Whiting wrote:
Scott wrote:

FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
LOT more than unleaded auto! Therefore, the 100 octane valves should
be supper lubricated! But, in fact, the 80 octane valve tend to stick
if much 100LL is run through them...

So, somebody answer my question...what is special about 100 octane
valves? The ones I put in my A-65 were Stellite. What does Stellite
do? What about sodium filled valves? What's their claim to fame??

Scott


Matt Whiting wrote:

Scott wrote:

Like I said, MIGHT OK, if there is no difference in heat, what
are the 100 octane valves in my A-65 for? Or more generally, why do
they sell 100 octane valves for A-65s and C-85s, etc. that were
certified on 80 octane??? Like I said, I use them, I don't wrench
on 'em



Because valves that were designed to be lubricated by the lead in
leaded fuel may not last long when using fuel with no or less lead.

Matt



No kidding. What's your point? I know that 100LL has a lot more lead
than 80. That doesn't change the correctness of my statement.

Matt

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

"Matt Whiting" wrote in message
...
Bob Fry wrote:
"Scott" == Scott writes:

Scott One thing I think "might" be a concern is that burning
Scott 100LL (can't get 80 octane avgas these days) in an engine
Scott built for 80 octane is the extra heat. Eh? Where's this
"extra heat" come from? There is no practical unit
energy difference between different octane fuels.

Some believe that higher octane gasoline burns more slowly and thus can
put more fire past the exhaust valve. However, most of my reading on the
subject suggests that this is a myth and there is no substantial
difference in burn rate as a function of octane.

Matt

I have not had occasion to test this premise on an aircraft engine--since
only 100LL was available when and where I flew. Therefore, no comparison
was possible.

However, back in the "bad ol' days", running a "regular gas" automobile
engine on "hi-test" had much the same effect as running with the ignition
timing retarded relative to that called for in the manual--the engine ran
noticeably warmer. Therefore, I am fairly certain that Big John is correct
in his assessment (elsewhere in this thread).

There is also the oft' stated issue of lead fouling, and it is possible that
the 100LL valves have some greater immunity to that as well; although I am
neither an engineer nor a wrench turner and I really have no idea how that
might be accomplished.

Peter

Now that's getting to the info I'm asking. So, I should probably call
my valves stellite valves rather than 100 octane valves. Does being
harder make it harder for lead to stick to the stems? Maybe THAT's why
I need stellite (100 octane) valves...to keep them from sticking when
using 100LL??? That's why I went to stellite -- to keep my valves from
sticking (two tanks of 100LL and I stuck one valve and could not get it
unstuck)...

Scott


Dale Alexander wrote:

Stellite is a very hard metal that does not transfer to the seating metal.
Valves and seats that are made of stellite do not wear at anywhere the rate
that older materials would. Use of hardened materials is one of the reasons
that contemporary engines (such as Toyota's) do not require a valve
clearance adjustment for the first ONE-EIGHTH of a MILLION MILES!!!

Elemental Sodium metal is liquid at temperatures that are common in a valve
stem. It is used in specially constructed valves that have hollow stems. As
the valve heats up, the Sodium becomes liquid. Now the trick is that the
hollow portion of the valve stem is not completely filled with Sodium. When
the valve opens,the Sodium will fill the end of the valve head (inside the
combustion chamber). Here it acts as a heat sink soaking up heat from the
exhaust gases as they exit the cylinder. When the valve moves to seat
itself, the heated Sodium moves to the valve stem area where the heat picked
up in the valve head area is transfered to the valve guide. This back and
forth transfer of heat helps keep the valve cool.

The downside of a Sodium filled valve is that the valve stem becomes quite
large. Because of this and the fact that better materials are now available,
they are not used on smaller bore engines as the increase in valve stem size
acts to reduce the amount of port area (in a critical area) needed to move
airflow in a high RPM engine. But in an inefficient aircraft engine where
heat is a larger concern that power, Sodium valves can be found.

Hope this helps,

Dale Alexander

"Scott" wrote in message
.. .

FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a LOT
more than unleaded auto! Therefore, the 100 octane valves should be
supper lubricated! But, in fact, the 80 octane valve tend to stick if
much 100LL is run through them...

So, somebody answer my question...what is special about 100 octane valves?
The ones I put in my A-65 were Stellite. What does Stellite do? What
about sodium filled valves? What's their claim to fame??

Scott


Matt Whiting wrote:

Scott wrote:


Like I said, MIGHT OK, if there is no difference in heat, what are
the 100 octane valves in my A-65 for? Or more generally, why do they
sell 100 octane valves for A-65s and C-85s, etc. that were certified on
80 octane??? Like I said, I use them, I don't wrench on 'em


Because valves that were designed to be lubricated by the lead in leaded
fuel may not last long when using fuel with no or less lead.

Matt

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)




--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

OK, this is where I probably made my wrong assumption (even though I
precluded my original post with the word "might" when referring to more
heat from 100 octane). So it's not heat produced strictly because of
higher octane, it's just that the mixture may still be burning as the
exhaust valves open on the exhaust stroke and "burns" the valves. So,
it may not burn hotter, but it seems to burn longer, thus heating the
valves more, so it's kind of semantics since the valve is still getting
hotter by burning 100LL rather than 80 (but for a different reason than
I originally posted and ****ed everyone off by regurgitating an old
wive's tale). Is this correct?

Scott



Big John wrote:

On Tue, 11 Dec 2007 01:55:38 +0000, Scott
wrote:


FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
LOT more than unleaded auto! Therefore, the 100 octane valves should be
supper lubricated! But, in fact, the 80 octane valve tend to stick if
much 100LL is run through them...

So, somebody answer my question...what is special about 100 octane
valves? The ones I put in my A-65 were Stellite. What does Stellite
do? What about sodium filled valves? What's their claim to fame??

Scott


Matt Whiting wrote:

Scott wrote:


Like I said, MIGHT OK, if there is no difference in heat, what are
the 100 octane valves in my A-65 for? Or more generally, why do they
sell 100 octane valves for A-65s and C-85s, etc. that were certified
on 80 octane??? Like I said, I use them, I don't wrench on 'em


Because valves that were designed to be lubricated by the lead in leaded
fuel may not last long when using fuel with no or less lead.

Matt



Scott

High octane fuel burns slower in low compression engines. This lets
the flame front go out the exhaust valves and burn them if you run a
lot of hours.

We ran into this in the 'old' days when the fighters used 115-145
octane fuel. If we used that fuel in our cars we had to mix some oil
with it to prevent the burnt valves.Occasionally someone would burn a
tank full to clean their engine out (burn carbon off cylinders and
valves, etc)

This is probably the reason they put 100 octane valves in your low
compression engine so you could use 100 octane and not destroy the
valves?

Big John

--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

"MW" == Matt Whiting writes:

MW Scott wrote:
FOUL!! 100LL has 4 times the lead content than the old 80
avgas and a LOT more than unleaded auto! Therefore, the 100
octane valves should be supper lubricated! But, in fact, the
80 octane valve tend to stick if much 100LL is run through
them... So, somebody answer my question...what is special
about 100 octane valves? The ones I put in my A-65 were
Stellite. What does Stellite do? What about sodium filled
valves? What's their claim to fame?? Scott
Matt Whiting wrote:
Scott wrote:
Like I said, MIGHT OK, if there is no difference in heat,
what are the 100 octane valves in my A-65 for? Or more
generally, why do they sell 100 octane valves for A-65s and
C-85s, etc. that were certified on 80 octane??? Like I said,
I use them, I don't wrench on 'em


Because valves that were designed to be lubricated by the lead
in leaded fuel may not last long when using fuel with no or
less lead.

MW No kidding. What's your point? I know that 100LL has a lot
MW more lead than 80. That doesn't change the correctness of my
MW statement.

Your statement may be correct but is irrelevant. The OP asked "what
is different about valves designed for 100LL in an engine originally
designed for 80 octane avgas (which has a fraction of the lead as
100LL). You answered the reverse question.
--
All natural institutions of churches, whether Jewish, Christian, or
Turkish, appear to me no other than human inventions, set up to
terrify and enslave mankind, and monopolize power and profit.
~ Thomas Paine

"DA" == Dale Alexander writes:

DA Now, what would 22K BTU stuff do in an 7 1/2 to 1 aircraft
DA engine? Probably nothing as the lower compression would limit
DA the amount of work actually being done.

If I can reword your statement to "what would higher octane stuff
do..." then I can answer not probably, but definitely, it will not do
anything different, if the only difference between the two fuels is
octane.

DA But it will still burn
DA hotter than a fuel with a lower BTU content.

Where did the difference in "BTU content" (i.e. unit chemical energy
content) come from? Not from a mere octane enhancer. Perhaps the
fuels used in your road racing experience had not only different
octanes, but also different unit energies.

Eh? Where's this "extra heat" come from? There is no
practical unit energy difference between different octane
fuels. --


Exactly. "Octane" is, by definition, a measure of a fuel's
resistance to knock under specific conditions. "High Octane"
fuel does not burn any hotter, generate any more power, or
improve your fuel economy (note: see exception below). Higher
octane fuel lets the engine designer use a higher compression
ratio, or more spark advance, etc. without triggering knock. It
is the compression / spark changes that result in more power,
etc.




--
"He is not only dull himself; he is the cause of dullness in others."
-Samuel Johnson

Octane and BTU are two different qualities of fuel. In a very simplistic
view, the longer the molecule, the more energy it takes to break it. By
needing more energy to break, it is more resistant to knocking or detonation
(not the same but still applicable). This would be octane.

BTU is the amount of energy that the chemical reaction will produce AFTER
the reaction has started. Compression, or lack of it, would reduce the
amount of pressure thus heat that the reaction would ultimately make. In a
system that is optimized (tuned) all of the heat energy possible may be
extracted. But even in a lower compression engine, an increase in heat would
be available as there is more potential in the first place. So no, the only
difference is NOT octane.

As I said, very simplistic but serves to illustrate the point.

By the way, I seem to remember a research paper that stated that
conventional motor fuels (not alcohol or nitro based, just for
clarification) burn at the same rate no matter the octane. I think that
confusion exists here in that a previous poster stated that higher octane
fuels burn slower. A lower octane fuel may "seem" to burn faster, but what
may be happening is that the normal flame front increases the pressure in
the remaining unignited mixture to the point of self-ignition and the
resulting second flame front advances to meet the first in a reduced period
of time. Still burning at the same rate but from two different starting
points and meetin gin the middle. This is abnormal combustion though and in
a normal combustion event, the fuels would burn at the same rate.

"Bob Fry" wrote in message
...
"DA" == Dale Alexander writes:

DA Now, what would 22K BTU stuff do in an 7 1/2 to 1 aircraft
DA engine? Probably nothing as the lower compression would limit
DA the amount of work actually being done.

If I can reword your statement to "what would higher octane stuff
do..." then I can answer not probably, but definitely, it will not do
anything different, if the only difference between the two fuels is
octane.

DA But it will still burn
DA hotter than a fuel with a lower BTU content.

Where did the difference in "BTU content" (i.e. unit chemical energy
content) come from? Not from a mere octane enhancer. Perhaps the
fuels used in your road racing experience had not only different
octanes, but also different unit energies.

Yes, the fuels used were different and proprietary blends that I was not
privy to. I was just a comsumer, not a business partner. But the fuels were
blended for specific purposes using various chemical qualities to achieve
end results. This I stated previously.

It seems that ERC is still in business. See

http://www.ercracingfuels.com/sxs1.htm

for a comparision of various blends. It would appear that their ERC MUL/A is
the fuel that I used in my motors and the ERC 1-19A is the 120 octane stuff.
But look around the website and find that various fuels do not have a direct
relationship between octane and BTU. So something other than octane is
definitely going on here. Read some of the descriptions of the bases and
blending to see what qualities they build the fuel for.


Eh? Where's this "extra heat" come from? There is no
practical unit energy difference between different octane
fuels. --

See above




Exactly. "Octane" is, by definition, a measure of a fuel's
resistance to knock under specific conditions. "High Octane"
fuel does not burn any hotter, generate any more power, or
improve your fuel economy (note: see exception below). Higher
octane fuel lets the engine designer use a higher compression
ratio, or more spark advance, etc. without triggering knock. It
is the compression / spark changes that result in more power,
etc.


You are correct that optimization of the engine as you mention will result
in more power, mileage etc. But we learned that you have to watch out for
the BTU as well. And an engine can generate too much heat and power to the
point of reducing power without ever suffering from pinging, knocking or
detonation. But that is a subject for another day.

I love this group! It would be great to sit down to a dinner conversation
with many of you. A lot of accumulated knowledge in this group..

On Dec 10, 2:32 pm, "RST Engineering" wrote:
Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
BY A HIGHER OCTANE FUEL.

Jim
----------------------------------------------------------------------------------------------

Gee, Jim... that can't be right. Because if it IS, it means 99 &
44/100% of the 'experts' out there are WRONG...

:-)

wrote:

On Dec 10, 2:32 pm, "RST Engineering" wrote:

Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
BY A HIGHER OCTANE FUEL.

Jim
----------------------------------------------------------------------------------------------


Gee, Jim... that can't be right. Because if it IS, it means 99 &
44/100% of the 'experts' out there are WRONG...

:-)


That's just about right...